RESONANCE IN ORGANIC CHEMISTRY.
By George Willard Wheland '28. New York:Wiley if Sons, 1955- 846 pp. $15.00.
"It is considered possible for the true state of a molecule to be not identical with that represented by a single classical valence-bond structure, but to be intermediate between those represented by two or more valence-bond structures." This statement of a concept which is central to the theory of resonance is also a concise description of a theory which had its origins in the latter half of the last century when it first became apparent that the chemical properties of some substances, notably benzene and its derivatives, could not be represented adequately by conventional molecular structures. The resonance theory has had striking success in dealing with such situations, and its importance can scarcely be overemphasized when we recognize, with the author, that the remarkable advances of chemistry in the past one hundred years have been closely associated with the development of a successful structural theory.
Since the publication of The Theory ofResonance (Wiley and Sons) in 1944, the name of George Wheland has been closely linked with resonance by chemists here and abroad. The present book, like its predecessor, deals explicitly with the interpretation of organic chemistry from the resonance viewpoint and presupposes a sound background in elementary organic and physical chemistry and in modern valence theory. The same basic organization has been retained. Thus, the first two chapters develop qualitatively the general principles of resonance and valence which are then applied, in the next six chapters to the specific topics of resonance energy, steric effects, dipole moments, molecular spectra and chemical equilibrium and kinetics. The new final chapter presents "those elementary aspects of quantum mechanics that are necessary for an understanding of the mathematical basis of both the resonance and molecular-orbital theories." The word elementary should not be read too literally; the average organic chemist will find these one hundred-odd pages good for more than several quiet evenings of work.
Likewise new is the parallel treatment accorded the molecular-orbital approach and the advantages and limitations of each theory are thoroughly and precisely discussed. The table of bond lengths and angles has been expanded some ninefold, while throughout the text new tables have been added and old ones revised. New sections have been added and old ones amplified, for example in the chapter on resonance energy. The literature used to document the discussion has been selected through 1954 and analyzed critically. Finally, and characteristic of the author, a determined effort has been made to eliminate or to clarify by detailed explanation much of the unprecise and often misleading terminology which has plagued this theory beyond its due to the detriment of much oral and written discussion.
In sum, the student of this book will be treated to a stimulating, detailed and authoritative analysis of an important and active field of investigation, written by an accomplished organic chemist and mathematician who has made many significant contributions to our understanding of resonance theory. Not the least of his accomplishments is the ability to write in an easy and lucid style which is all too rare in the scientific literature.
